With their excellent characteristics taken advantage of, epoxy resins have been widely used in various applications including coatings, adhesives, civil engineering, and construction. However, most of them are of two-pack type and provide poor workability on use. One-pack systems can be obtained by using a latent curing agent such as dicyandiamide, a catalyst capable of generating radicals on UV irradiation whereby to cure an epoxy resin, an acid anhydride curing agent, and the like. Nevertheless such techniques involve heating for cure or require equipment for UV irradiation. Moreover, cured products obtained from these one-pack systems are generally poor in flexibility.
A curable epoxy resin composition containing a ketimine as a curing agent is known as a one-component, room-temperature curing system free from the above disadvantages. A ketimine reacts with moisture supplied from the outside to produce an amine by which to cure an epoxy resin. Epoxy resin compositions making use of this system are disclosed in JP-A-63-273629 and JP-A-63-273630. However, the proposed epoxy resin compositions have poor storage stability, or need a modified silicone resin for obtaining a flexible cured product, or, when applied to a general-purpose epoxy resin, provides a hard cured product unless the formulation is narrowly limited.
JP-A-5-132541 proposes a polyoxyalkylenediamine-based ketimine compound. When a low molecular weight polyoxyalkylenediamine-based ketimine compound specifically disclosed in the publication is used alone, the resulting epoxy resin composition has insufficient adhesion to a substrate. When, on the other hand, in using a high molecular weight polyoxyalkylenediamine-based ketimine compound alone, the resulting epoxy resin composition has insufficient curability. In addition, the process of preparing the ketimine compound according to JP-A-5-132541 has difficulty in obtaining a desired ketimine compound at a high degree of ketimination, only to provide an epoxy resin composition having poor storage stability.